Photographic color developer



Patented July 2, 1940 UNITED STATES PATENT OFFICE 2,206,126 PHOTOGRAPHIO COLOR DEVELOPER Karl Schinzel, Groppau, Czechoslovakia, assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of lflew Jersey No Drawing. Application April 29, 1931, semi No.139,'l58. In Austria May 9, 193a te m.. (01. 95-88) images in photographic layers.

In one of the well-known prior art methods, in

which the oxidation product of an ordinary'dei5 veloping agent, formed on development, couples with a color-forming compound, the colored images produced are not always clear, due to the condensation or oxidation of several molecules of the developer. 1 have found that this ,objectiong9 able feature may be overcome .to a large extent by using an excess of coupling component in the developer solution. The developing solution,

, consisting of a 1 to 2% solution'of the developing agent, should contain 3 to 5times the amount of 3 coupling component theoreticallyrequired to couple with the developer, as well as sodium carbonate, trisodium phosphate, borax, sodium bicarbonate, sodium glycocoll, etc., in addition to the ammonia or other alkali necessary for the 30- solution of the phenol or naphthol couplers.

I have found, however, that the most favorable results in three-color reversal and redevelopment are obtained with simple color developers which I are oxidized to the insoluble, or at least non-dif- 5 fusing, dye by the exposed silver halide or that made developable in any other manner, as by bleaching to a halide after development. Two main groups-are included: (A) Those in which two equal molecules-of the developer are combined to the dye, that is, auto-couplers. (B)

Those which can be regarded as leuco-form. of

solution containing sodium carbonate yielded in-.

tensely.lemon-yellow images, unless the exposure was too weak. The p-chlorand p-brom-deriva- Id tive also develop with formation of the lemonyellow quinone imide, but only slightly with the p-cyano-derivative also .examined. Since the new dye iscompletely stable to acids and .alkalies and is insoluble in lye, a 1-2% alkaline solution of this o-amlno-phenol can "serve as developer.

Addition of sulfite is unnecessary, as the solution can be easily preserved. The rapidity of reaction can be increased, if in additon to the fixed alkali absolutely necessary for solution, also sodium carbonate is added or the developing solu- 1'0 ,tion is prepared at once with an excess of ammonia. A dilute alcoholic solution could; of course, also be used for development. The.p-' halide derivatives seem to develop somewhat more rapidly. 'P-amino-m-xylenol suggested and 15 very useful as a developer does not seem to pro duce color images, although its a1kaline-solution precipitates a yellow dye after some time.

' Numerous other o-amino-phenols in alkaline solution, constructed analogous to the Auwer dye, 2

are suitable developers, as for example, 0- amino-m-broiir-m-cresol, which produces reddish-yellow images. Similar images also are produced by o-amino-m-xylenol while the o-amino isopseudocumenol which is unfortunately very difllcult to prepare yields brilliant lemon-:yellow images. Red to purple color images may be ob-' tained with different chlor and bromderivatives of o-aminophenol, and other m*-substituted oaminophenols as: 3-methoxy-o-aminophenol, o- 3 amino-rresorcin-monoalkyl ether ,and the analogous resorcine derivatives, as well-as with m-hydroxy-p-amino-dialkylaniline. Even the simplest o-amino-phenol yields reddish-yellow to orange images with development in a solution containing sodium carbonate or alkali, according to the dispersity of the dye or of the original silver halide. Homologuesproducing mostlyredimages are better suited, as for example o-amino-m-cresdl in a so- I lution containing sodium carbonate, or'its br'omderivative, as well as fi-amino cresol. It is very interesting that o-methylaminophengl and o- .ethylamino-phe'nol, less satisfactory as developers, yield o-phenoxazine quinones by alkaline I oxidation. Amldol is also said to yield red-brown 4 dye images (Photographische Korrespondenz 1896/6344) Experiments, however, showed that they were too weak; diamido-o-cresol. behaves similarly; Numerous other quinone imides are formed during development with the correspond- 5o ing diamino phenols or. amino hydroquinones. Simple aminophenols and also aromatic p- 'or odiamines are less inclined to precipitate insoluble oxidation products.

Amongthe heterocyclic compounds as for ex- 35 kaline solution. It is of greatest theoretical in.

terest that also 3-phenylamino-s-naphthol develops to a purple color image, provided the sample used .is not made impure by the presence of isomers. 4-amino-1: Z-dihydroxy-naphthalene yielding in development the red 2-hydroxy a naphthoquinoneimide (hydroxlmido- 'naphthol) and diaminonaphthols of different;

constitutions are less suitable.

Formation of a yellow dye during development with the mono-carboxylic acid of lz-i-dihydroxy naphthalene is an exception.

Lignone dyes.Blue to purple lignones can be considered as analogues of the indigoid dyes. Their simplest representative is diphenoquinone which cannot be obtained by development. It is, 1

however, rather easy to prepare their substitution products by oxidation of two molecules of the corresponding generators by means of the exposed silver'halide. It was found that the long known orange-yellow coerulignone is produced not only during development with an alkaline solution of pyrogallol dimethylether, but also in development with hydrocoerulignone, and that a red-yellow image also remains after removal of the silver with Farmer's solution. The alkaline or ammoniacal solution of pyrogallol dimethylether is remarkably stable in comparison with that of hydrocoerulignone; it is not atmospheric oxygen, but the exposed silver halide alone, which eflects the formation of the lignone dye. Similarly colored images at least with well-exposed silver chloride, are formed by vicm-xylenol. These orange-yellow tones are, however, of less importance in color photography. Purple-red lignones are formed in developmen with oo-dichlor-, dibromand also diiodinephenol ,probably only in alkaline solution, al-

though these dihalide phenols are also soluble in.

sodium carbonate. It is interesting that also two molecules of tri-iodine phenol can be condensed .naphthalene (a-naphthhydrdquinone) produces an intensely blue color image after development of the latent image in alkaline solution and removal-of the silver'formed by Farmer's reducer; the image consists of the so-called Russig dye. 2-mono-alky1 ether of 1:2-dihydroxy-naphthalene, however, easily prepared from the i-diasoderivative by exposure, yields a purple-red image. The mono-ethers of -iz4-dihydroxy-anthracene form a 'green'dyeimage during photographic de velopment, the mono-ethers of 1,2-dihydroxyanthracene a more -brick-red image.

The presence of alkoxy-groups in-the 2- or 4- position of a-naphthol is by no means a necessary condition tor the formation oi lignone dyes during development. It appears that any group is suflicient which cannot easilybe reduced, among which are the phenyl residue, because 2-phenyl-- s-naphthol yields purple part images in alkaline" developer solution, whereas its tetra-methoxyderivative, easily prepared irom papaverine, peculiarly forms a blue lignone dye.

The relatively high stability of the lignone generators in solution prepared with the theoretically required amount of alkali or ammonia seems to justify synthetic preparation oi further representatives of this class of dyes.

Principally, the mono-ethers oi the 1:4- or 1:2- dihydroxy-derivatives can be prepared from other higher aromatic ring systems, possibly with a heterocyclic ring attached, also oi those in which a ring, not substituted by lignone-i'orming groups,

. is entirely or partially hydrated; this especially holds true for anthracene. The developing ability remains intact, ii alkoxylation of one hydroxyl is not accomplished by methylor ethyl residues, but by higher aliphatic alcohols, benzylor phenyl-ethyl alcohol etc.. also by phenyl and other aryls. Esterincation can be accomplished by first allowing ethylene oxide to react in the required amounts with one hydroxyl group, followed by esteriflcation of the hydroxyl groups in the hydroxyl-alkyl ether by means of the chicrides of aliphatic or aromatic acids in the presence oi tertiary bases; it necessary, the aromatic hydroxyl group is first converted into the easily split carbethhydroxy-derivative. It is often better to attain this object in other ways, for example by substitution of the halide in theibromor z-brom-a-naphthol by the phenol'resi- A due with sodium phenol in the presence 01' copper bronze. One can allow p-toluol sulfochloride to act on the ethers by 4- -amino-a-naphthol'in the presence of tertiary bases or other agents, whereby an arylsulfonylamine group of the same char acter as aromatic hydroxyl is formed. Red

images are formed during development in alkaresidue,-esteriflcation or the aliphatic hydroxyl group and arylsultonylation ot the amino group can be accomplished together by using an exces's o! p-toluol sultonchloride. Aminoand hydroxyl groups can be introduced into the phenyl residue or the second nucleus of 2-phenyl-s-naphtholor also the monoethers of 1:2- and' 1:4-dihydroxynaphthalene mentioned, and this can be combined by acylation, alkylation, arylation and other synthetic operations with the difierent aromatic or heterocyclic systems. This is often connectd with a tar-reaching change or the color, as can be seen by comparison with lignons from 2 -phenyl-a-naphthol and its tetra-methoxy derivative.

Generators of indiaoid dyea aenuine vat dyes are often considerably superior to the lignones in stability, and many of them can be generated by condensation through oxidation 01' two equal molecules of their generators during photographic development. The generator'is dissolved in the amount or lye or ammonia theoretically required, if necessary, mixed with an excess of so-=' dium carbonate, unless it is soluble in sodium car- An almost unlimited number of generators is. available or can be synthesized theoretically for the production of blue, green-blue and purple vat dyes in this manner; nevertheless, the choice of suitable yellow developers is very limited, that is, a true lemon-yellow developer. is not available at all, unless barbituric acidis considered as generator of the lemon-yellow intermediate form of the so-called urindigo. Cumaranone in aqueous sodium carbonate solution, uniortunately,. does not yield the lemon-yellow images corresponding to hydroxindigo. The carbindigo formed during development with a sodium carbonate solution of '4-hydroxyiso-carbostyril is colored strongly redyellow, ii .it is finely divided in gelatine, in the substance it is a pronounced red. 'I'he'practical--- that of hydroxy-seleno-naphthene which is re-.

markably stable also in alkaline solutions, coloring only weakly red. The purple color of selenindigo almost corresponds to the theoretically required, not substituted thio-lndigo, and comspondingly substituted indoxyls canbe used in development for obtaining of green-blue indigos. The corresponding naphthalene (thio) iridoxyls yield naphthene indigos, and naphthalene thioindigos of the same shade. The red-violet tone of 6,6'-dihalide indigos formed in development with the correspondingly substituted indoxyls are of practical importance because then the use of hydroxy-seleno-naphthene or substituted thioindigo for the formation of the purple part image appears unnecessary, and no reduction of the dyes formed previously in the other layers is to be feared. 1 Alsothe N-alkyland aryl-derivatives 01' indoxyl, its N-acyl derivatives, phenylthioindoxyl and its nitroand amino derivatives, phenylhydroxythiophene are much more stable in alkaline or sodium carbonate solution than indoxyl and thioindoxyl', so that they are more suited for photographic purposes, even if the purity of the indigos formed has not yet been proven. Alkaline solutions oi-o-mercapto-acetophenone are still more stable; although it is gradually oxidized to thioindigo by atmospheric oxygen; it is, therei'ore, also worth considering as red developer. some oi the (thio) indoxyls derived from anthraquinone and benzathrone excel for their stability. Also suliurylindoxyl is dimcult'to oxidize to sulfurylindigo similarly pyridindoxyl.

B. Leuco due developers pyrindoxyl and thioonly those are considered which are converted into a completely insoluble quinone during development oxidation, while a certain solubility in water is desirable with the corresponding hydroquinone, so that it may also be used in sodium carbonate solutions,

The principal yellow developers are the multiple-arylated hydroquinones in alkaline solution, as zzi-diphenyl-lizfi-dibenzylhydroquinone,

- droxynaphthalene,

2:5-.dixylyl-hydroquinone, 2:5-di-p'-tolyl-hydro-' 'quinone, 2:5-di-p-phenetyl-hydroquinone. .Octohydrogenated anthrahydroquinones, easily prepared in small amounts by Skita, deserve spe-- cial attention, and vespeciallythe p-methyl-derivative soluble in alkali, tor the production of yellow dye images which can also be obtained with the hydrogenation product of 1:4-anthraquinone. The eilfect ofi'a fl-stable amino group changing the-color oi the hydrogenated quinone to red, is noteworthy. It is best developed in dilute alcoholic solution according to Glaisen. One could, oi course, also here return through acylation of the amino group to the original color 0! the non-substituted quinone or to a still more suitable color.

Similarly partially hydrogenated higher quinones 'can also be obtained by combination or unsaturated hydrocarbons with naphthoquinones and anthraquinones. Also 2- phenyl-a-naphthol-hydroquinone, diphenoxy-hydroquinone and many others yield yellow images.

Many of the numerous free and acylated, alkylated or arylated amino-, hydroxy mercapto derivatives, etc., of benzoand naphtho-quinone's, as well as of higher quinones also with heterocyclic rlngs attached and mentioned in literature,

are useful in color photography. The ,corresponding hydroquinones have been prepared from most of them, in as much as the latter could not be obtained with the formerly-used reducing agents, on account of their low stability, this is now accomplished in most cases by catalytic reduction in a properly selected medium. If acyl-- ation, alkylation, arylation etc. of the substituted.

groups has not been done at the beginning, it may sometimes also be accomplished in the tinished quinone in order to prevent the simulment in solution containing sodium carbonate oralkali, unless atmosphericioxygen is excluded, not considering the fact that also the amino quinones formed sometimes are inclined to poly merization with formation oi: blackish products.

Also .tor theacylamino hydroduinones which are in themselves stabler, one ri ust only take the amount of alkali ,iust'necess'ary for solution in order to prevent attacking oi 'the gelatine. This sometimes seems to make the use of ammonia necessary. In the naphthalene group often those amlnohydroquinones excel byf eater stability in which the substitution is in the second nucleus. While o-quinones oi the benrol series are only seldom easily prepared, p-ngi'phthoquinones can be formed during photographic development, it the 4-position of 1:2-dihydroxy-naphthalene is fixed by alkyl-, aryl-, acyl-, acylamino-, ketone groups, etc.,- so that the great tendency to iormation of z-hydroxy-u-naphtho-quinone (hydroximino-naphtho) is stopped.

For. example, the'aminoand acylamino hydroquinones' among which are phenyldiaminohydroquinone, phenylmethyl-iminazol-p-naphtholquinone also d-acetamino- 1:2-dihydroxy naphthalene, I 2 acetamino 3 'chlor-lzl-dihy- 1 droxynaphthalene, 2:8 diacetamino 1:4-dihy- 3:5. diacetaminohydroqiiinone, etc., are especially noteworthy. I

The brominated hydroquinones', such as'adurol,

also tri and tetra-chloroquinone, are suitable for sci on them in the presence of copper bronze then they are reduced, if necessary. In this manner, yellow, blue to purple substitution products were obtained from thymoquinone. The condensation products with malonic ester, etc., are also worth mentioning further dichlor-a-naphtho-quinone with thioindoxyl and. amines and similar condensation products of which the yellow naphthiminazolqulnone from 2-amino- -3-chlor-k4- dihydroxy-naphthalene, whose deep-blue alkaline solutions yield lemon-yellow 4-arylazo-p-naphthoquinone in the development of the latent image, are in a group by themselves. it is mentioned thathydrazo forms of a-naphthol azo dyes could be prepared in individual cases and also serve as developers. The reduction can often be accomplished without splitting of the azo group by catalysis with palladium and hydrogen at ordinary temperature and higher pressure, also with o-azodyes.

Leuco vat dues as. dev'elopers.--The leuco-indophenols which in many respects belong here, as well as leuco-indamines and leuco-azomethines may be sufficiently stable in alkaline solution to serve as developers, the finished dyes are, however, rather easily decomposed by acids. Also the reduced lignone dyes of the type of hydrocoerulignone or of the hydrated Russig dye are diilicult to handle on account of the strong inclination to reoxidize the dye by atmospheric oxygen and'the tendency to fog resulting from it. Jacobson, in his detailed investigation of the most favorable working conditions with hydrocoerulignone and i-hydroxy-isocarbostyryl (Atelier des Photographen 1929/86-89), recognized that these substances are as little suitable for practical color" development as fndoiwl, thioindoxyl, etc.

This criticism, must, however,-not be generalized, either in regard to the leuco-bodies conearned, or to the type of test conditions. Even 'tetra-chlorand tetra-brom diphenols are dissolved without color in' lye or sodium carbonate, a sign of their indifference to atmospheric oxygen, and they yield fog-free purplecolorimages in development. It is peculiar that the reduction product of tetra-iodine-diphenoquinone,

easily obtained from tri-iodiiie phenol ,by alkaline oxidizing agents, is insoluble in lye. The

leuco-formof the lignone from two moleculesof tetra-methoxy-phenyl-a-naphthol in less degree of tetra-methyl-diphenoquinone' and of their analogues, are similarly stable.

- The leuco-forms of the genuine vat dye used in vat dyeing are. very easily. reoxidized in alkaline solution. Pure thioindigo white and selenoindigo, white can xbe preserved for a long time.

mmense is less durable, a dilute alcoholic solution of the'same is immediately dehydrated to indigo by platinum-black, also anthrahydroqulnone, of course, with absolute exclusion of In conclusion several centimeters high impoured film is-covered by a protecting sheet .which is reoxygen. Among the indigoid and analogous vat dyes there are much more stable leuco-derivatives, as: NN'-dimethyl indigo white of certain highly-halogenated thio indigos, if they are reduced in the presence of too little ,alkali, or of those which form difllcultly soluble alkali salts, as is the case with dinaphthacridonequinone with anthraquinonethioxanthones and other anthraquinone dyes, tetra -hydrofiaventh'rene' and its red dimethoxy, as well as the green acylamino, derivatives dihydrophen-anthridlne yellow and its golden-yellow dimethyl derivative. 'Thlonyl indigo white which is oxidized to th dye only by hydrogen peroxide and alkali; NN' diphenyl indigo white, NN-dimethyl indigo white, 2:2- dibenzoyl thioindigo white, leuco-pyrindigo, the lemon-yellow diisobarbituric acid from 5-aminouracile, the hydrated dinaphthacene dlquinohe, diamino-binaphthylene dioxide, the completely or partially reduced dibenzothianthrene diquinone dihalide-perylene-Z:IO-hydroquinones, dibenzoylamino-9: lfl-perylene hydroquinone are especially stable. Many amino-anthraquinones, also acylated ones or those with heterocyclic rings attached, or substituted by alkoxyor arylhydroxylor acylh'ydroxy-groups, are reduced by many reducing agents or catalytically to the anthranol or anthrone form. It was found that not only the derivatives of anthrahydroquinone, but also those of the anthranol form are capable of developing the latent image. If the reduced dye is in its anthrone form, it is converted into the alkaline salt of the anthranol form bywarming with lye or, if necessary, by addition of alcohol, and the anthranol form is used for development. Images of the lemon-yellow dianthrone are obtained with the salt of dianthranol. Tetrahydro-helianthrone is constructed very analogously and to tetranhydroxy-helianthrone. The

leuco-forms of the condensation products from two molecules of indoxyl, thio-indoxyl, hydroxyselenonaphthene, etc., with one molecule of an aliphatic, also unsaturated or aromatic dialdee hyde are somewhat stabler than those of the genuin indigo dyes.

Until now it was questionable, whether indigo white, and with it leuco-vat dyes, have developing power at all. Liesegang 1895 stated that indigo white (or its sulfonic acid, Jahrb. 1. Ph. 1896/48'7) is able to produce a strong black image and also Abribat confirmed this later, but Lumiere and Seyewetz found that it must'be ascribed to an impurity of ydrosulfite' or ferrosuliate. None of these auth s has investigated, whether in- ,digo is also formed.

,in a test-tube with aqueous alkaline hydrosulfite solution on which a layer of benzol or petroleum The exposed moved only after passing the petroleum layer, otherwise development hardly takes place. Nobody will deny that such a developing method is inconvenient for the amateur and the professional. But in motion-picture technique where the fihn is developed by automatic machines. this 7 ficulty is easily overcome, allowing air-sensitiv amount. may also be added to aqueous solution substances to be used for color photography. The

' air in the developing apparatus is replaced by nitrogen or any other indiilerent gas, also illuminating gas may be used in case of emergency, or the apparatus is installed in a room filled with such a gas and the operator must wear a gas mask with air supply. This method of working is not only recommended when using leuco-vat dyes, indoxyl, thioindoxyl, etc., or hydrated quinone dyes, but also in the usual black development of motion picture films, since by this method large quantities of valuable developer substance and sulflte are saved which otherwise are lost by oxidation from the air. It is understood that in" color development with vat dyes and for washing, boiled or distilled water should I,

be used, in order to avoid color fog. The preparation of vat solutions or other air-sensitive developing solutions is, of course, also done without oxygen, after which it is filtered and placed in 'As little hydrosulflte as possible should be used; the excess can be converted by addition of formaldehydeor better non-tanning-aldehydes into Rongalite or similar substances whichcannot be developed any 7 more. This is not absolutely necessary, since also in the presence of hydrosulflte sufllciently strong color images are formed. This method of working is also advisable in the production of colored images by means of coupling developers,

as for example, a-naphthol and p-amido-dimethylaniline, in order to avoid. color fog. -It is sometimes recommended not only to fill the developing apparatus with inert gas, but also to cover the solutions with a layer of petroleum or other liquids which do not attack the film.

Alkaline or possibly ammoniacal solutions of the vat dyes are usually considered for the formation of the last, as a rule middle, image only, be-

cause most of them reduce unexposed silver halide also, unless very much potassium bromide or a few percent potassium iodide'are added to the developer. The principal'methodof making silver halide emulsions developable is, of course, by thiourea, etc., or reducing to silverierrocyanide, For colored development of the two other emulsions vat solutions are usable, since in indoxyl and its derivatives and analogues easier eneration of the vat dyes is available.

Also here, 1-2% solutions are used.

When using leuco-vat dyes and their generators, one should consider that some of them in alkaline solutions have the ability to reduce the dye already formed 'on the image. Alkaline indigo white solutions, 'for example, or vat dyes formed onwa'rming of halogenated indigo or thioindigo which is even capable of reducing itself to the leuco form may be used. Color lution of a highly halogenated indigoid dye, which contains no excess alkali or at the most only sodium carbonate. When the lower part image has developed to indigo or more greenish derivatives of the same, themiddle image can be developed purple with the aid of the redto redviolet 6,6-dihahde indigo or its leuco-form.

Ammonia is recommended to use for the solution of the vat dye, because this does not attack the gelatine, even with a slight excess, as much as fixed alkali does. Alcohol or acetone in any 'be developed by an aqueous suspension of indigo white or thioindigo white, which are dissolved in small amounts; if necessary, this may be used after addition of potash or sodium carbonate. In this case, also the'relatively stable, even it diflicultly soluble,'magnesium'salts of leuco vat dyes can be used for developmentas also the dimcultly soluble alkali salts of the various highly halogenated indigo and thioindigo dyes, and of some higher molecular vat dyes. Also purely aqueous suspensions or solutions of the leuco forms in alcohol or acetone reduce silver chloride made developable by exposure, or by thiourea, through prolonged action with absolute exclusion of atmospheric oxygen, or after addition of arcmatic amines.

I It may happen-that the dye formed in the color development is not entirely insoluble in water, but at the same time so persistently adsilver of the lower emulsion can be first removed.

without harm.

In the U. s. Pat. 1,076,301 it is stated that m each color development oi! the latent image'the emulsion is not completely developed out, but a ,residue is left behind which reacts to a certain degree with the next 'color' developer, so that -fresh developer, or by finishing development with an ordinary black developer which has no cou-- pling ability and also cannot contain sulflte, if indophenol or azomethine dyes are used. After washing, the next color development is done. In

order to be absolutely sure, one could also bathe in potassiumferricyanide after each part color development, but only for such a short time that only the residues of the previous latent image are destroyed, the reduced silver, however, [not essentially attacked. Since careful washing of all traces of ferricyanide is necessary in order to avoid color fog, and also occasionally the (color) sensitivity must beregenerated by a following bath of sulflte, bisulilte, hydrazine or hydroxylamlne etc., the whole color process is'retarded and made more expensive.

The color developers must not necessarily be pure. but may also contain other non-color-developing or coupling developer substances'in order to reduce the intensityoi'the color image and to obtain the correct gradation in respect to the other part .color imageaby the relational, the ,5

rapidity oi both developers in this mixture or to the coupling tendency of the one. r In reversal development, it isrecommended to use those primary developers which do not form desensitizing oxidation products, since these do not always remain on the place or their origin,

-but also are capable of diffusing. This efiects later exposures oi. residual or regenerated silver halide in the same or adjacent emulsion. Iron oxalate developer of normal composition is well suitable. The general opinion that a residual' image of such developer oxidation products is indispensibleim the formation of correctly graduated reversal images, does at least not apply for the triple layer with its thin layers oi silver -bromide'gelatine. For this reason it is also recdimer quinone imide dyes are, according to Auwer, very resistant not only to acids, but also to reducing agents, they can serve for the production of the yellow and also of the purple lower part image, while the middle image is formed by direct development with a strongly actin leuco-vat dye. In films coated on both sides, two leuco-vat dyes can be used independently from each other, one for each side, while the third art color image is developed with another color developer. If the triple layer contains a silver chloride emulsion, the second color development can also be done. with a vat solution. it the silver chloride remaining from the preceding development has been converted into the more resistant silver terrocyanide; in reversal and redevelopment it can then be reduced to the last part color image by a strong leuco-vat dye, eitherdir'ectly or aiter'reconversion into silver chloride.

printing or optical printing of three-color images.-

uniiorm gradation can be obtained by the use of difierent color filters or variation oi. the exposure. In black part negatives, one prints first with colored light 'on the sensitized middle layer imd then with ultra-violet light on the two other avers.

Several possibilities'ior recording negative or positive sound in variable density or variable width exist. With white light, one can print on all three layers, so that it finally appears black, or

it is printed on only one or two layers and developed in color and then exposed to complementary light for reproduction. The photo cell must, however be sensitive to this light.. In order to protect the vsound strip against damage, it is best to print it in the lower emulsion. This is especially advantageous in reverse order of the layers where the blue-sensitive layer adjoining the support consists of highly dispersed sensitized silver halide and the following yellow filter acts as antihalation, it one prints with blue light. Besides, in a normal triple layer, a fourth, approximately grainless, silver halide emulsion could be arranged which is sensitized ior infrared, so that printing and developing take place independently from the others. Printing is done optically through the back. if the anti-halation layer is transparent to infra-red. Printing can be done after drying also in any stage of the coloring process. The sound strip can be arranged as in modern processes as multiple variable width, as combination of the variable density and variable width, etc.

It is to be understood that I consider the various modificationsand examples or the foregoing specification, whether claimed or not, as included within the scope of my invention; and I desire to secure by Letters Patent of the United States, protectioncn all the novel subject matter disclosed herein.

I claim: 7 I

l. A photographic developer comprising a compound selected irom the. group consisting of 1:2 dihydroxy anthracene compounds, 1:4 dihydroxy anthracene compounds, and alkyl monoethers of 1:2 and 1:4 dihydroxy anthracene in a weakly alkaline solution, the developer being capable of forming a colored image in, an exposed gelatinosilver halide emulsion layer.

2. A photographic developer comprising a compound selected from the group consisting of 1:2 dihydroxy anthracene compounds, 1:4 dihydrolw anthracene compounds, and alkyl monoethers of 1:2 and 1:4 dihydroxy anthracene in a 1 to 2% solution of an alkali, the developer being capable of forming a colored image in an exposed gelatino-silver halideemulsion layer.

3. A photographic developer comprising an alkyl-ether of a dihydroxy anthracene selected from the group consisting of 1:2 and 1:4-dihydroxy-anthracenes in a weakly alkaline solution, the developer being capable of forming a colored image in an exposed gelatino-silver halide emulsion layer.

4.v A photographic developer comprising an alkyl ether of a dihydroxy anthracene selected from the. group consisting oi 1:2 and 1:4-dihydroxy-anthracenes inn 1 to 2% solution or an alkali, the developer being capable of forming a colored image in an exposed gelatino-silver halide emulsion layer. v.

, KARL SCHINZEL. 

